1. Field of the Invention
The invention relates to a diagnosis management system for a valve-controlled hydrostatic displacement unit and to a diagnosis management method performed with such a diagnosis management system.
2. Description of the Prior Art
Hydrostatic drives, comprising a hydropump which drives a hydromotor via a fluid line, have in the meantime gained wide use in mechanical and systems engineering but also in the automotive field. Among the hydraulic or hydrostatic displacement machines or hydromachines used in this field as drives are pumps and motors, which operate on the displacement principle and as a rule have the same structural layout. By suitable control of the fluid flow, pumps in particular can function as motors, and vice versa. Because of the distinction in the direction of action, it is true of so-called hydropumps that they convert mechanical power into hydraulic power, and for so-called hydromotors that they convert hydraulic power back into mechanical power.
Recent drives, which are suitable particularly for vehicles, are digital displacement machines, which operate on the principle of digital displacement and are predominantly embodied as multi-cylinder pumps and/or multi-cylinder motors or multi-cylinder pump motors, for instance as radial piston engines. In such engines, each cylinder has at least two valves, such as cup valves, slide valves, combination valves, and the like, of which one is a low-pressure valve communicating with a low-pressure fluid, and the other is a high-pressure valve communicating with a high-pressure fluid, and a microcontroller reads out a piston position or shaft position sensor and controls one or more of the valves. A hydraulic motor is attained when the high-pressure valve is triggered as well.
While the aforementioned type of drives has considerable advantages, particularly in the automotive field, or in other words for motor vehicles, in that case for instance as a gear-axle drive unit, such as a fast response speed and inherent energy efficiency from high efficiency, nevertheless it lacks diagnostic capabilities and evaluation logic units for errors in the control part, especially of the hydrostatic valve-controlled displacement unit or digital displacement unit, and more precisely for errors in the power electronics employed there. This is because until now, in a triggering chain, an FPGA (Field Programmable Gate Array) has been used as an array of logic gates that can be configured in the field of application and that operates on the order of a port expander. Here, the FPGA receives bus signals only from a controlling microcontroller, transfers them within a predeterminable length of time to corresponding end stages, and thus triggers those end stages. Thus signals are forwarded in only one direction to the digital displacement unit to be controlled, and no diagnosis or feedback signals are provided. Because of the lack of feedback between the components, sources of error can be located only with difficulty. The FPGA itself is furthermore vulnerable to malfunction and difficult to analyze. Finally, the use of FPGAs in the automotive field might not be permissible in every case.
Accordingly, the known triggering chain for a digital displacement unit, which is based on the use of an FPGA, has no diagnostic capabilities, so that errors cannot be detected, no information exchange between the components of the triggering chain can take place, and thus in the system no reactions to any errors in the system can take place. Hence there is a problem, in that a higher-order control and/or regulating system in the event of error will receive no information about the type and severity of the error in the digital displacement unit. The result can be damage in components, lines, and the like—those that carry pressure, for instance. Until now, errors in the system could be detected only by experience with the system in operation, so that expensive system maintenance was furthermore disadvantageously absolutely necessary.